This invention relates to a method of electrolytically decomposing an iron-cyanide complex.
Waste water from a carburizing process for iron, plating or printing process, photograph processing or the like contains an iron-cyanide complex, the content of which should be desirably reduced in the waste water from an environmental standpoint.
The iron-cyanide complex, however, is relatively stable and is not conveniently dissociable in an aqueous solution because of low dissociation constant of iron-cyanide complex, for example those for potassium ferricyanide and ferrocyanide in the orders of .times.10.sup.-44 and .times.10.sup.-33, respectively. Further, the iron-cyanide complex shall not be decomposed chemically even by addition of a strongly oxidizing agent unless the high temperature is employed for the decomposing reaction.
It has been well known that an addition of alkali to such the aqueous solution to obtain the strong alkalinity enables the ultraviolet-light irradiation to decompose the iron cyanide complex. This decomposing reaction, however, needs a considerable energy with an oxidizing agent as an additive to decompose the liberated cyan, resulting in a complicated and high cost process.
Further, it has been proposed to utilize the sun light in place of the ultraviolet-light in order to reduce the cost. At present, however, the decomposing method of this type is not practical for a diluted solution because of its low efficiency and more time-consuming.
On the other hand, it has already been experienced that a heavy metal salt in a plating solution could be electrolyzed for recovery of the metal. An attempt to utilize this electrolytic method for the decomposition of the iron-cyanide complex and the oxidization of the liberated cyan into a cyanic acid, however, could not provide a practical method because of extremely low efficiency in the decomposition.
It has now been found out that in the method of electrolytically decomposing an iron-cyanide complex, an oxidative decomposition does not substantially develop if the specific conductivity (.kappa.) of the electrolyte exceeds about 30 m /cm, whereas the decomposing reaction may occur moreeasily as the specific conductivity (.kappa.) decreases below the above upper limit.